The present invention relates to systems for the conveyance of unitized loads, such as transfer conveyors. More particularly, the invention pertains to an apparatus for removing a dunnage sheet from beneath a unitized load.
Many products are shipped using waste or dunnage material to protect stacked product. For instance, as shown in FIG. 1, dunnage material D protects a load L that is contained by an array of straps S. The load may be, for instance, multiple stacks of sheet material, such as corrugated sheet or paperboard blanks used in making boxes. The corrugated sheets are shipped flat in a stack about 72 inches high. The strap S is typically a plastic band that is tightened and clamped about the load stack. When it is desired to remove the load L from the waste sheet the straps S are typically manually cut and removed as the load travels along a load conveyor (FIG. 3).
When the load L is sheet material, such as the corrugated sheet mentioned above, dunnage or waste sheets D are added to the top and bottom of the load stack. The dunnage sheets D are provided to protect the surface and edges of the uppermost and lowermost sheets of the load stack. The dunnage sheets are therefore wider than the load so that the sides of the dunnage sheets D may be folded over the edge of the load. In a typical load of sheet material, multiple stacks are supported on one common dunnage array. In this case, the dunnage sheets D are sized to cover every stack and the straps S are sized and arranged to firmly hold all the stacks together.
When a unitized load of sheet stock is received, the unit is dropped on a load conveyor (FIG. 3). As the unitized load progresses along the conveyor, the straps S are cut and removed. The top dunnage sheet D is also removed so that the load L is free and available to be fed to a pre-feeder, as shown in FIG. 3. In certain systems, when the load L is prepared, a transfer device moves the load off the load conveyor and onto a transfer conveyor that leads to the sheet pre-feeder. At the pre-feeder, various operations are performed on the load, depending upon the nature of the pre-feeder and downstream processing stations. In some devices, the multiple load stacks are converted to a single stack, the stack(s) is inverted, smaller stacks are removed, etc.
The lower dunnage sheet poses a problem, especially for multiple stack loads. When the straps S are removed, the flaps F of the bottom dunnage sheet D tend to fall away from the load L, as shown in FIG. 2. Unless the dunnage sheet is removed prior to reaching the pre-feeder, the sheet may foul the operation of the pre-feeder. In most cases, the load L is too heavy for manual removal of the bottom dunnage sheet from underneath the load. Thus, an apparatus is required to mechanically remove the dunnage sheet without disturbing the multiple stack load and without unduly disrupting the process flow from the load conveyor to the pre-feeder. In one approach, a reverse running gum belt is situated at the transfer device (FIG. 3). A gate is lowered to hold the load L while the reverse running belt spins to slip the dunnage or waste sheet out from under the load. This approach requires essentially stopping the load while the retention gate is lowered and the reverse running belt operated to strip the dunnage sheet. Another problem is that this system typically only removes the lowermost dunnage sheet, so any additional dunnage sheets would remain undisturbed with the load. In another approach, the leading edge of the dunnage or slip sheet projects ahead of the load and is engaged by a mechanism that pulls the slip sheet away from the load as the mechanism is moved out of the path of the load.
What is needed is a dunnage sheet removal apparatus that may be easily integrated into an existing conveyor system and that performs its function without any significant disruption of the process flow from the load conveyor to the pre-feeder. There is a further need for a dunnage sheet removal apparatus that is capable of removing virtually any type and any number of waste sheets.